Ion implanters can be used to treat silicon wafers by bombardment of the wafers with an ion beam. One use of such beam treatment is to selectively dope the wafers with impurities of a controlled concentration to yield a semiconductor material during fabrication of a integrated circuits.
A typical ion implanter includes an ion source, an ion extraction device, a mass analysis device, a beam transport device and a wafer processing device. The ion source generates ions of desired atomic or molecular dopant species. These ions are extracted from the source by an extraction system, typically a set of electrodes that energize and direct the flow of ions from the source. The desired ions are separated from byproducts of the ion source in a mass analysis device, typically a magnetic dipole performing mass dispersion of the extracted ion beam. The beam transport device, typically a vacuum system containing an optical train of focusing devices transports the ion beam to the wafer processing device while maintaining desired optical properties of the ion beam. Finally, semiconductor wafers are implanted in the wafer processing device.
Batch processing ion implanters include a spinning disk support for moving multiple silicon wafers through the ion beam. The ion beam impacts the wafer surface as the support rotates the wafers through the ion beam.
Serial implanters treat one wafer at a time. The wafers are supported in a cassette and are withdrawn one at time and placed on a support. The wafer is then oriented in an implantation orientation so that the ion beam strikes the single wafer. These serial implanters use beam shaping electronics to deflect the beam from its initial trajectory and often are used in conjunction with co-ordinated wafer support movements to selectively dope or treat the entire wafer surface.
Faraday cups are used to measure beam current. These cups are periodically inserted into an ion beam either upstream of the implantation chamber or at a region behind a workpiece support to monitor beam current. U.S. Pat. No. 6,992,309 to Petry et al. illustrates a dosimetry system having a Faraday cup that is mounted for movement along a controlled path. The disclosure of the '309 patent is incorporated herein by reference.